MEK1/2-dependent induction of BIM phosphorylation after stimulation with anti-IgM. (A) CLL samples and (B) Ramos cells were cultured in the presence or absence of U0126 (10μM) for 1 hour before stimulation with anti-IgM. Expression of BIM, phospho-ERK1/2, and β-actin was analyzed by immunoblotting. Open arrowheads indicate phosphorylated BIM forms. Data are representative of a total of 6 CLL samples and 3 independent Ramos cell experiments.